Unusual structural evolution of poly(lactic acid) upon annealing in the presence of an initially oriented mesophase.

Uniaxial deformations of amorphous poly(lactic acid) (PLA) films were performed at two different temperatures, 70 and 80 °C, at various draw strains. The samples deformed at 70 °C showed a strain-induced mesophase, and the structural ordering and thermal stability increased as the draw strain increased. Further annealing was performed in situ at constant length at the drawing temperature of 70 °C for the films drawn to strains of 100% and 230%. Unusually, we found that after annealing, the crystal structure of the film at lower strain was more ordered than the one at higher strain. Further investigations revealed that upon annealing the structural evolution followed a distinct molecular mechanism for the samples stretched to the two draw strains. For the sample drawn to 100%, the mesophase melted very quickly upon annealing, resulting in chain randomization and the release of the constraints on the thermodynamic relaxation of the oriented amorphous chains. The chain relaxation motions had a beneficial effect on the occurrence of the conformational rearrangements that are necessary for crystalline ordering. By contrast, for the 230% sample, the melting of the mesophase was slow and most of the chain orientations were preserved upon annealing. As a result, a less ordered crystal structure was formed since the local relaxation motions that are necessary for promoting crystalline order via conformational rearrangements were hindered.

Lipase-catalyzed ring-opening polymerization of natural compound-based cyclic monomers.

The need for sustainable and environment-friendly materials has led to growing interest in the development of biodegradable polymers based on natural compounds. However, metal-based catalysts used in the polymerization process may cause concerns about the toxicity of the resultant polymers. Therefore, polymers derived from natural compounds and synthesized through the use of green catalysts are highly desirable. Lipase-catalyzed ring-opening polymerization (ROP) of biocompound-based cyclic monomers has emerged as a promising and green strategy for the design and synthesis of such polymers. In this review, we summarize reports on the use of ROP catalyzed by lipase for cyclic monomers derived from natural compounds, including bile acid- and porphyrin-based macrocycles, carbonate-based macrocycles, lactones, and cyclic anhydrides, with an emphasis on ring-closure reactions for the synthesis of cyclic monomers, the types of lipases for the ROP and the choice of reaction conditions (temperature, solvent, reaction time, etc.). Moreover, the current challenges and perspectives for the choice and reusability of lipases, ring-closure versus ring-opening reactions, monomer design, and potential applications are discussed.

Aggregation-induced emission luminogen with excellent triplet-triplet upconversion efficiency for highly efficient non-doped blue organic light-emitting diodes.

By combining aggregation-induced emission (AIE) effect and a triplet-triplet upconversion (TTU) process, a blue emitter with excellent photoluminescence quantum efficiency and high upconversion efficiency in the film state is developed, from which a highly efficient non-doped blue TTU organic light-emitting diode (TTU-OLED) was realized.

Simultaneously achieving high capacity storage and multilevel anti-counterfeiting using electrochromic and electrofluorochromic dual-functional AIE polymers.

With the advent of the big data era, information storage and security are becoming increasingly important. However, high capacity information storage and multilevel anti-counterfeiting are typically difficult to achieve simultaneously. To address this challenge, herein, two electrochromic and electrofluorochromic dual-functional polymers with aggregation-induced emission (AIE) characteristics were rationally designed and facilely prepared. Upon applying voltages, the absorption and fluorescence spectra of the AIE polymers can undergo reversible changes, accompanied by variation of their color and emission. By utilizing the controllable characteristics of the polymers, dual-mode display devices were fabricated via a simple spraying technique. More interestingly, a four-dimensional color code device was constructed by adding color change multiplexing to the two-dimensional space, thereby achieving high capacity information storage. Moreover, the color code device can also be applied in the multilevel anti-counterfeiting area. The encrypted information can be dynamically converted under different voltages. Thus, the AIE polymers show great promise for applications in multidimensional information storage and dynamic anti-counterfeiting, and the design strategy may provide a new avenue for advanced information storage and high security technology.

Highly Efficient Amide Michael Addition and Its Use in the Preparation of Tunable Multicolor Photoluminescent Polymers.

The amide bond is one of the most pivotal functional groups in chemistry and biology. It is also the key component of proteins and widely present in synthetic materials. The majority of studies have focused on the formation of the amide group, but its postmodification has scarcely been investigated. Herein, we successfully develop the Michael additions of amide to acrylate, acrylamide, or propiolate in the presence of phosphazene base at room temperature. This amide Michael addition is much more efficient when the secondary amide instead of the primary amide is used under the same conditions. This reaction was applied to postfunctionalize poly(methyl acrylate-co-acrylamide), P(MA-co-Am), and it is shown that the amide groups of P(MA-co-Am) could be completely modified by N,N-dimethylacrylamide (DMA). Interestingly, the resulting copolymer exhibited tailorable fluorescence with emission wavelength ranging from 380 to 613 nm, which is a desired property for luminescent materials. Moreover, the emissions of the copolymer increased with increasing concentration in solution for all excitation wavelengths from 320 to 580 nm. Therefore, this work not only develops an efficient t-BuP4-catalyzed amide Michael addition but also offers a facile method for tunable multicolor photoluminescent polymers, which is expected to find a wide range of applications in many fields, such as in anticounterfeiting technology.

Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles.

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials.

Biocompound-Based Multiple Shape Memory Polymers Reinforced by Photo-Cross-Linking.

For the design of shape memory polymers with potential biomedical applications, we synthesized methacrylate-based monomers bearing biological compounds such as cholic acid and cinnamic acid in addition to oligo(ethylene glycol) as pendant groups and opted to use a simple radical polymerization method for the preparation of the copolymers. The glass transition temperatures of these polymers are broad and tunable and can thus accommodate dual and triple shape memory behaviors. The fixity ratios of dual and triple shape memory are all above 91%. The recovery ratio of dual shape memory is 89.5%, whereas the two recovery ratios of triple shape memory are 53.2 and 81.5%, respectively. To further improve the shape memory properties, a cinnamic acid-based methacrylate monomer was incorporated into the copolymers to enable a photo-cross-linking of the terpolymer. After irradiation, the fixity ratios remain high, whereas the recovery ratios of dual and triple shape memories are much improved. The terpolymers after light irradiation even show quadruple shape memory property. Different irradiation times were tested to optimize the shape memory effects. The recovery ratio of dual shape memory of such terpolymers can reach as high as 98.6%, whereas the recovery ratios of triple and quadruple shape memories are improved to the range of 75.3-99.1%.